Electrical circuit



March 27, 1951 D. D. COFFIN ETAL 2,545,181

ELECTRICAL CIRCUIT Filed Feb. 13, 1947 3 Sheets-Sheet 1 45 LOHD OVER K560149710 M/I/E/VTM' mwa 0. car/71v Bf/FIVHRD L. 6 Mr Maid! 951 D. D. COFFIN EIAL 2,545,131

ELECTRICAL cmcum Filed Feb. 13, 1947 3 Sheets-Sheet 2 March 1951 D. D. COFF |N ET AL 2,546,181

ELECTRICAL CIRCUIT Filed Feb. 13, 1947 3 Sheets-Sheet 5 am/la 0. CUFF/M BER/V080 A 696/1 Patented Mar. 27, 1951 ELECTRICAL CIRCUIT David D. Coffin, Newton Highlands, and Bernard L. Cook, Medford, Mass, assignors to Raytheon Manufacturing Company, corporation of Delaware Newton, Mass., at

Application February 13, 1947, Serial No. 728,282

6 Claims. 1

This invention relates to electrical circuits for stabilizing the output of non-linear devices, and more particularly to the output of such devices generally referred to as magnetrons.

The main object of the present invention is to provide electrical circuit means capable of maintaining the radio frequency power output of a magnetron constant irrespective of the load impressed thereacross or of any variation in the line voltage.

The above and other objects will become more evident as the description of the present system progresses, and reference is had to the drawings accompanying same, in which:

Fig. 1 is a partial block and partial schematic diagram of the control portion of the system of the present invention;

Fig. 2 is a graph illustrating the phase relation of applied grid voltage to the output of the rectifying circuit of the present system;

Fig. 3 is a graph illustrating the relative amount of current output in accordance with the phase relations shown in Fig. 2;

Fig. 4 is a vector diagram illustrating the range of phase shift available in accordance with the present invention and the magnitude of the ap-' plied grid voltages shown graphically in Fig. 3; and

Fig. 5 is a schematic diagram of the protective portion of the present system.

Referring now more particularly to Fig. 1 of the accompanying drawings, the numeral l8 refers to a source of alternating voltage which is applied, respectively, to a pair of primary windings I l and i 2 and an over-regulated alternating voltage regulator l3.

Current flowin in the primary ll induces a current in a secondary winding 14, cooperating therewith, to produce a very high alternating voltage. This last-named voltage is in turn applied via conductors l5 and IE to the input junctions H and I8 of a bridg type rectifier circuit 19. The rectified output of said bridge circuit is taken from the output junctions 23 and 2! thereof and applied to a load 20A via conductor 22 and conductor 23, resistor 24 and another conductor 25. Said load 20A may be, for example, an electron-discharge device such as a magnetron.

When current flows through the load 20A, a potential will be developed across the resistor 24 of a magnitude depending on the amount of current flowing through said resistor. This potential is used to oppose a second source of potential in a manner to be explained presently.

Said bridge type rectifier circuit 19 consists of,

for example, a pair of gaseous discharge diodes 26 and 21', each of said diodes including, respectively, anodes 28 and 29 and cathodes 30 and 3i and a pair of grid controlled gaseous discharge devices 32 and 33, known to the art as thyratrons, said devices including, respectively, anode 34 and 35, control grids and 31, and cathodes 38 and 39.

The anodes 28 and 23 are connected to one of the output junctions 2i and the cathodes 38 and 33 of the thyratrons 32 and 33 are connected to the other output junction 2|. The cathodes 30 and 3! of the diodes 23 and 27 are connected, respectively, to the anodes 34 and 35 of the thyratrons and to the respective input junction l1 and 58.

Referring again to the primary winding i 2, said winding induces a current in a secondary winding 46, cooperating therewith, to produce a voltage, which in turn is impressed on the grids 36 and 3'? through a phase-shifting network 4!.

The Voltage from said network will appear across resistors 42 and 43 between points A and B. These last-named resistors are connected from point C to the junction 2! and are so arranged as to provide voltages between points AC and BC that are 180 degrees out of phase with respect to each other. This out of phase arrangement for supplying control grid voltages to the thyratrons 3233 provides means for firing said thyratrons in phase with the alternating potential applied to the anodes 3435 from the secondar winding 14.

A pair of resistors 44 and 45 serve, respectively, to limit the flow of current to the grids 36 and 31 and a pair of capacitors 46 and 41 serve to by-pass any radio frequency currents to ground.

The phase-shifting network 4! includes in selies with the secondary winding 40, a resistor 48, a capacitor 59 and the saturable winding 50 of a saturable reactor 5|. With the aforesaid components it is possible to achieve a phase shift somewhat less than degrees. This is due to the fact that a saturable reactor has a variable Q and as a result the phase-sh ft range is therefore limited. However, by including in parallel with the aforementioned components a capacitor 52 and a resistor 53, there is provided, by the present invention, a novel phase-shifting arrangement having a range substantially in excess of 180 degrees. Phase shift is accomplished automati"ally by altering the inductance of the winding 50 as will be presently explained.

A direct-current potential is supplied to the saturable reactor 5| by the rectified output of a The over-regulated alternating voltageregulator provides means whereby, for any given increase in the line voltage Iii, this regulator will automatically decrease the output voltage there from by a value greater than the given increase and vice versa. For example, if the line voltage I should increase, say from 1 to 1l5 volts, the

regulator will decrease the output from 115 volts down to 105 volts. The reason for using this type of regulation will be discussed below. 7 v t Let it be assumed that it is desired to maintain, substantially constant, a radio frequency output with an input to the magnetron of the order of one ampere when the thyratrons are prevented from firing for about 45. This phase relation will be further explained in connection with the graps of Figs. 2 and 3. v

In the present system, there are present two variables, namely, line voltage and the load current. If either the line voltage varies or the load current changes, it is the purpose ofthe present invention to automatically compensate the 1 system to maintain a predetermined ave-rage input to the load. If, for example, the system of theipresent invention be used in connection with high-frequency cooking, various foods will require different cooking. periods. However, it is essential that, for good cooking operation, theradio frequency energy for the period selected be constant or the food will be either overdone or vice versa. H

Because various foods have differing dielectric constants, their e-ifect on the load A, when placed in the field generated thereby, will vary the current through said load. Again, assume thatthe change thus brought about causes a decrease in said current. Consequently this decrease in the current through the load 20A will result in a decrease in the potential drop across theresistor 24.. H Now, as pointed out before, the combination of the potential drop across the resistor 24 and the potential developed across the saturating winding 54 of the saturable reactor 5| serves to alter the flux in the core of said reactor and consequently the inductance of winding 50. In the particular embodiment described herein, by way of illustration, the potential developed across the winding 54 is always of a higher order than the potential drop across the resistor 24. Therefore, ad'ecrease in the potential across the resistor 24 will provide an increase in the difference po tential across the winding 54 and an accompanying decrease in the inductance of winding 50. As a result, the phase will shift in such a direction as to increase the conduction of the thyra- 'trons 32 and 33 and consequently increase the I magnitude of the current through the load 20A.

The relation of phase shift to current flow in said 'thyratrons will be explained in more detail in connection with Figs. 2 and 3. I

Referring now to Figs. 2 and 3 in which the reference numeral I20 represents a half cycle of anode voltage, which may be, for example, the anode voltage of one of the thyratrons 32. The grid control locus I2I represents the magnitude of voltage which, relative to the anode voltage curve I28 above it, is sufficient to prevent firing of the thyratron The'base line I22 represents the time axis, and the sine curves I23, I24 and I25 represent instantaneous values of applied grid voltages which appear across either pair of points, for example, AC of the phaseshifting network 4I, since the discussion will be with respect to the operation of the thyratron 32.

A novel feature of the present invention resides in the fact that as the phase is altered from M to N and from N to O, the amplitude of the instantaneous applied grid voltages I23, I24 and I25 increases and by these means crosses the grid control locus I2I at substantial angles thereto as illustrated by the points P, Q, and R. Were it not for this particular phase-shifting network and the arrangement of the components thr'edf, as described earlier herein, as the phase ofthe instantaneous grid voltages advanced, without an accompanying increase in amplitude, the grid voltages would not intersect the grid control locus IZI continuously from the beginning of the half cycle of the anode voltage I20 curve to the end thereof. Instead, as said grid voltages were advanced in phase they would not intersect the grid control locus I2I at point R, for example, and the result would be limited control of the thyratron 32. t M

Fig. 3 indicates more clearly the time during which the current fiows in the thyratron 32 for each instantaneous value and phase of grid voltage; the shaded portions I26, I21, and I28 indicating the duration of current flow. As the current through the load 20A decreases, it is desirable to approach the condition indicated: by the numeral I25 while, if the current through the load increases, it is desirable to approach the condition, for example, as represented by the shaded area I28. As either of the aforementioned conditions are corrected, the normal condition will be as represented by the shaded area- I21.

In Fig. 4, the graph illustrates a locus which indicates the development of aseries of grid voltage vectors X, through- X5, as the inductance of the saturated winding 55 is altered in accordance with the earlier description of this system, and it-can be readily observed that as said vector'rotates through the points I32 to I36, a phase shift rangein excess of degrees is quite possible. However, in the particular embodiment, useis made of only about 1 50 degrees of phase shift. The vectors K through X5 are developed in the following manner:

Let it be assumed that the voltage across the winding 43 is a predetermined electrical length as indicated by the vector I31. To achieve a phase shift of the order above described, a capacitor 52 and resistor 53 are shunted across the secondary winding 49, and the potential drops across saidcapacitor and resistor noted. The vector X represents the potential drop across said capacitor 52 while the vector X0 represents the drop across the resistor 53. By inscribing an arc whose radius from a point D is' equal in length to the vector X0, and then intersecting. said lastnamed are with another arc, whose radius extends from a point E equal], in length, to the vector X, the position of point A is established.

To determine the course of the locus B, a plurality of points I32I36 are developed as follows:

There is now induced in the winding 54 a current, by any suitable means, which will alter the inductance of the winding 50 due to the change in the amount of saturation of the core of said saturable reactor 5 I. Potential readings are now taken as represented, for example, by the vector X11, the potential drop between points B and D and the drop between points B and E being represented by the vector X12. As in the case of the vectors X and X0, the intersecting arcs subtended by the radius of the vectors X11 and X12 establish, for example, the point I32. The remaining points I33-I36 are similarly developed and the locus B is thus established. From the point A the vectors X1-X5 are extended to the respective points I32I36. The respective lengths of said vectors X1X5 represent the magnitude of the voltage between points A and B as the phase of the network, including the elements 48, 49, 50, 52 and 53, changes.

A pair of terminals Z-Z, disposed in one of the conductors 5'! of the 110 volt alternating current source I0, and a pair of terminals Y-Y at the ends of the resistor 24, refer to points of connection to the protective circuit of the present invention as illustrated in Fig. 5.

Referring now to Fig. 5, the protective circuit comprises generally means for guarding against excessive current through the load 20A, which will appear across the resistor 24 and therefore between the terminals Y--Y. The excess current would result from a failure of the load 20A to produce a radio frequency output when the system is made operative. As pointed out hereinbefore, the load, in this particular embodiment, a magnetron, is used for the production of radio-frequency oscillations in the microwave region.

The excessive current protective circuit comprises a resistor 61, relay 62, and the winding 63 thereof which is in series with said resistor. Said relay may be, for example, a solenoid type having an armature 65 to which is attached a contact bar 66 for closing the gap between a pair of contacts Iii-68. A capacitor 64 is shunt-connected across the winding 63. The value of the resistor 6I is such that, under normal operating conditions of the load 20A, current through said resistor and the winding 63 of the relay 62 will be insufficient to operate said relay. However, should excessive current fiow through the resistor 24, a sufficient potential will be developed across points YY to cause the relay B2 to become operative and disconnect the line supply I0 as will be presently explained. The capacitor 64 should have a value sufiicient to delay the operation of relay 62, due to the initial current surge, when the system of the present invention is made operative.

The radio-frequency output protective circuit includes a resistor 69 in series with a second resistor I0 and the winding II of a relay I2. Said relay may be the same type as relay 62 and will include an armature I3, a contact bar 14, and a pair of contacts -19. A capacitor H, shuntconnected across the winding II, serves the same purpose as the capacitor 64 above described. Shunted across the resistor I0 and winding II is a gaseous discharge device I8, for example, a neon-filled diode. This gaseous discharge device is placed in the radio frequency field generated by the load or magnetron A.

Under normal operating conditions the value of the resistor 10 is such that a sufi'icient potential is developed thereacross to cause a slight ionization of the discharge device I8. As a result, the value of the resistance of the device I8 is such that the total potential developed across resistors 69 and I0 is insuificient to actuate the relay. However, should the current across the resistor 24 drop below a predetermined value, for example, due to a failure of the magnetron 20A to operate properly, but nevertheless above a predetermined minimum value, the potential drop across the resistor 10 will be lowered in accordance therewith. Consequently, the slight ionization of the device 18 previously referred to will diminish or substantially disappear and the resistance of said device increase an amount sufficient to inhibit the passage of current therethrough. As a result substantially all the current will now flow through resistors 69 and 10, the values of which are such that, under the aforementioned conditions, they will develop a potential thereacross sufiicient to actuate the relay I2 and interrupt the supply line voltage I0 in a manner which will be described below.

The aforementioned protective circuit, which is connected between points YY, operates in conjunction with a control circuit including the following:

A push button starting switch 19, having a pair of contacts and 8I for controlling the flow of current, in a manner which will be presently described, to a relay 82, is provided. Said relay may also be a solenoid operated type in-- cluding an armature 83 surrounded by a winding 84. The ends of said armature are connected to a pair of contact bars 85 and 86 for closing the circuits connected to a plurality of contacts 8'I88 and 89-90, said contacts being part of said relay 82.

One end 9| of said winding 84 is connected via a conductor 92 to one terminal 93 of a timing device or relay 94, which may also be solenoid operated, and to one of the contacts 95 of said timer, said timer having an armature 96 actuated thereby, said armature serving to close the gap between said contact 95 and a cooperating contact 91. The other end 98 of said relay 82 is connected via a conductor 99 to a second terminal I00 of the timer 94 and via a conductor I0! to one terminal of a source of potential I02, for example, a source of volt alternating current.

In this particular embodiment, the timer contacts 95 and 91 are normally closed subsequent to the manipulation of the switch I9. The contact 80 of said last-named switch is connected via conductors I03 and I04 to the other terminal of said potential source I02.

/Closing the starting switch I9 causes current from the source I02 to flow via the conductor I04 and the conductor I03 through the contacts 80--8I, through a third conductor I05, thence through a pair of contacts I06-I07 of a fifth solenoid operated relay I08, said contacts, under normal operating conditions, being closed as will be presently explained, and continuing from said contact I0! via a conductor I09, through the closed contacts 95 and 91 and thence through the winding 84 via the conductor 99 to the terminal I00 and through the conductor IOI backto the other terminal of the potential source I02.

As a result of the passage of current through the circuit as above described, the relay 82 and amen-oi 9 1 bothbecome. energized: The energizes tiofr of therelay 82" causes the: armature 83* to cl'o'se the contacts. Bl ds and 89-98. The clos of: contacts. ti -88' completes the circuit between the terminals Z-Zof Fig. 1 and thus en ergizes same; while the closing of contacts tit-sf closes-"the timer 3d circuit and sets the mocha" nisin of said. timer into operation. The closing of contacts 899d now replaces the starter sw itcn 1:9 contactsywhichareallowed to open fin- Inediately' after they are manipulated to initiate theaicregoing cycle. For a predetermined period the timer will maintain the contacts 555 and ill closed, and as long as these remain closed and the relay [93' remains deenergized, the relay 22 willremain energized and maintain a flow of current to: the circuit in Fig-. l Upon completron-or the timing cycle, the timer solenoid (not shown) becomes energized and opens" the contacts 55 and 9T by" drawing in the armature $5. This last-named action breaks the winding 8 circuit, and the contacts til-E38 and til-Pt are caused to open, thereby to interrupt the flow of current in the circuit of Flg. l.

Energization' of the relay it'd, whose winding H controlsthe actuation of an armature connected therewith, serves to interrupt the how of current to the relay 8?. by opening the contacts lil6=l-El 't and closing a pair of cooperating contacts Fil -H 2; in a manner which will be presently described.

In the event, first, of an excessive current condition during: operation of the main circuit of Fig. 1, brought aboutfor any reason whatsoever, such excess will of course manifest itself by an increase potential across the resistor 59 and thereby energizethe relay 52 through its winding 6-3,..causingi the armature 65 thereof to be drawn in and the contacts iii-E53 to close.

The closing of said last-named contacts will cause currentto flow from one side of the potential source I02 through conductor lei, conductor M3,. winding iii? of relay IE8; conductor H4 contacts 6'1-68, conductor H15, contacts fill-9t, which are closed during operation of the Fig. 1' circuit as previously explained,v a pair of normally closed contacts llfil ll of stop switch [15 to the other sideot the potential source Hi2. Said last-named stop switch may be used to interru'pt the operation of both the protective circult being. described and the circuit of Fig. l at any time.

Since. allof the actions of the aforementioned relays are substantially instantaneous, as soon as the relay iilii becomesenergized, it opens the contacts !Ei8-l0l and by so doing interrupts the timer; 9'4 and relay $2 circuit, causing the first to become inoperative and the relay to become deenergized.

In the case where a failure of radio-frequency generation occurs, the relay (2 is energized by theaction of the gaseous discharge device '58 as previously described; Since the contacts l-l6 are connectedin parallel with the contacts 67-68, the same sequence of events will occur, leading to the interruption of the system.

It will be noted from the foregoing that there has been provided an extremely simple and ef fective system for maintaining a constant output from anon-linear load such, for example, as the radio frequency-output of a magnetron. Said last-named circuit is further simplified by the elimination of rectified voltage filtering capacitors. Another feature of the system-of the present invention is the novel protective circuit used 8 in connection; therewith tol provide: the" utmost in protection of the equipment used.

Other advantages of the system of the present invention will occur to those skilled in the art'to which the same relates,v and it should be under stood that changes therein may be made with out the exercise of invention and within the true spirit and scope of the claims appended hereto.

What isclaimed is:

11 An electrical system comprising: a source of alternating voltage; means for rectifying a portion of said voltage; a non-linear device adapted tobe energized by said rectified voltage; means, operating on said rectifying means for controlling the-magnitude of the current applied to said non-linear device; means, connected in series with said non-linear device and rectifying means for developing adirect potential of predetermined magnitude; and-means, responsive to said direct potential, for disconnecting said source of alternating voltage when said direct potential exceeds a predetermined magnitude.

2 Anelectrical system comprising: a source of alternating voltage; means for rectifying a portion of said voltage; a non-linear device adapted to be energized said rectified voltage; means, operating on said rectifying means for controlling the magnitude of the current app-lied to said nonlinear device; and means, coupled to said nonlinear device, for disconnecting the source of alternating voltage when the output ofsaid nonlinear device falls below a predetermined magnitride.-

3. An electrical system comprising: a source of alternating volt-age; means for rectifying a portion of said voltage; a load device energized by said rectified voltage; first voltage-responsive means operating on said rectifying means for controlling the magnitude of said rectified voltage; second voltage-responsive means connected between said source andsaid operating means for controlling the voltage supplied to said operating means from said source, said supplied voltage varying in phase and amplitude in response to variations in the voltage applied to said second means; means, connected in series with saidload device and rectifying means, for developing a first unidirectionalpotential proportional to the current flowing through said load; means, connected to said source through an over regulated voltage regulator, for developing a second unidirectional potential which varies as the voltage of said source varies; and means for differentially combining said first and second unidirectional potentials to derive a difference potential and for applying said difference potential to said second voltage-responsive means to control the voltage supplied to said operating means.

4. An electrical system comprising: a source of alternating voltage; means for rectifying a portion ofsaid voltage; a load device energized by said rectified voltage; voltage-responsive means operating on said rectifying means for controlling the magnitude of said rectified voltage; a phase-shifting network, including a voltage-responsive variable impedance, connected between said source and said operating means for controlling the voltage supplied to said operating means from said source, said supplied" voltage varying in phase and amplitude in response to variations of said impedance; means, connected in series with said load device and rectifying means, for developinga first unidirectional-potential proportional to the current flowing through said load; means, connected to said source through an over regulated voltage regulator, for developing a second unidirectional potential which varies as the voltage of said source varies, and Whose magnitude is higher than said first unidirectional potential; and means for differentially combining said first and second unidirectional potentials to derive a difference potential and for applying said difference potential to said variable impedance to vary the same and thereby also the voltage supplied to said operating means.

5. An electrical system comprising: a source of alternating voltage; means for rectifying a portion of said voltage; a load device energized by said rectified voltage; voltage-responsive means operating on said rectifying means for controlling the magnitude of said rectified voltage; a phase-shifting network, including a saturable reactor, connected between said source and said operating means for controlling the voltage supplied to said operating means, said supplied voltage varying in phase and amplitude in response to variations in the control voltage applied to said reactor; means, connected in series with said load device and rectifying means, for developing a first unidirectional potential proportional to the current flowing through said load; means, connected to said source, for developing a second unidirectional potential which varies as the voltage of said source varies; and means for differentially combining said first and second unidirectional potentials to derive a difference potential and for applying said difference potential to said reactor as the control voltage therefor to vary the voltage supplied to said operating means.

6. An electrical system comprising: a source of alternating voltage; means for rectifying a portion of said voltage; said means including a bridge circuit having in at least two of its arms respective grid-controlled gaseous-discharge devices and in at least two of its arms respective high-vacuum discharge devices; a load device energized by said rectified voltage; the grids being voltage-responsive and operating on said rectifying means for controlling the magnitude of said rectified voltage; voltage-responsive means connected between said source and said grids for controlling the voltage supplied to said grids from said source, said supplied voltage varying in phase and amplitude in response to variations in the voltage applied to said voltage-responsive means; means, connected in series with said load device and rectifying means, for developing a first unidirectional potential proportional to the current flowing through said load; means, connected to said source, for developing a second unidirectional potential which varies as the voltage ofsaid source varies; and means for differentially combining said first and second unidirectional potentials to derive a difference potential and for applying said difference potential to said voltage-responsive means to control the voltage supplied to said grids.

DAVID D. COFFIN. BERNARD L. COOK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,027,235 Klemperer Jan. 7, 1936 2,101,802 Winograd Dec. 7, 1937 2,103,997 Bedford Dec. 28, 1937 2,299,942 Trevor Oct. 27, 1942 2,325,092 Andrews July 27, 1943 2,380,522 Haug July 31, 1945 

